Effect of the CuO addition on a Sb-doped SnO2 ceramic electrode applied to the removal of Norfloxacin in chloride media by electro-oxidation

Abstract

Norfloxacin is employed as in veterinary and human medicine against gram-positive and gram-negative bacteria. Due to the ineffective treatment at the wastewater treatment plants it becomes an emergent pollutant. Electro-oxidation appears as an alternative to its effective mineralization. This work compares Norfloxacin electro-oxidation on different anodic materials: two ceramic electrodes (both based on SnO2 + Sb2O3 with and without CuO, named as CuO and BCE, respectively) and a boron doped diamond (BDD). First, the anodes were characterized by cyclic voltammetry, revealing that NOR direct oxidation occurred at 1.30 V vs. Ag/AgCl. The higher the scan rate the higher both the current density and the anodic potential of the peak. This behavior was analyzed using the Randles–Sevcik equation to calculate the Norfloxacin diffusion coefficient in aqueous media, giving a value of D = 7.80 × 10−6 cm2 s−1 at 25 °C), which is close to the predicted value obtained using the Wilke-Chang correlation.

The electrolysis experiments showed that both NOR and TOC decay increased with the applied current density, presenting a pseudo-first order kinetic. All the anodes tested achieved more than 90% NOR degradation at each current density. The CuO is not a good alternative to BCE because although it acts as a catalyst during the first use, it is lost from the anode surface in the subsequent uses. According to their oxidizing power, the anodes employed are ordered as follows: BDD > BCE > CuO.